Cerebral pressure autoregulation is typically defined as the maintenance of a constant cerebral blood flow (CBF) in the face of changing cerebral perfusion pressure (CPP). In healthy individuals, this process protects the brain during transient changes in arterial blood pressure (ABP). However, various medical traumas, such as traumatic brain injuries, strokes, cardiopulmonary bypass, etc., may impair cerebral pressure autoregulation. Impairment of autoregulation narrows the range of blood pressures at which flow is matched to metabolic needs.
The brain's primary mechanism to maintain constant or nearly constant CBF is by varying the resistance associated with blood vessels supplying blood to the brain. For example, the brain may control the diameters of these blood vessels to allow the blood vessels to supply more or less blood to the brain, depending on the metabolic need. Therefore, vascular reactivity is an important component by which constant blood flow to the brain is maintained.
One current medical diagnostic method to measure or assess cerebral vascular reactivity generates a pressure reactivity index that uses intracranial pressure as a surrogate of intracranial blood volume, and detects passivity of blood volume to arterial blood pressure, which is used to indicate loss of vascular reactivity. Such methods, however, require complex monitoring devices, such as transcranial probes, that are cumbersome and difficult to maintain in the proper position on a patient to obtain accurate data, or intracranial probes that must be inserted into the skull of a patient. As a result, such methods may be ill-suited for use with many types of patients, such as patients in critical condition, pediatric patients, geriatric patients, etc.